Among the various video display systems available in the art, an optical projection system is known to be capable of providing a high quality display in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors such that each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of a baffle. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIG. 1, there is shown a cross sectional view of an M.times.N electrodisplacive actuated mirror array 10 for use in an optical projection system, wherein the actuators are made of a piezoelectric material, disclosed in a copending commonly owned application, U.S. Ser. No. 08/246,891, entitled "PIEZOELECTRIC ACTUATED MIRROR ARRAY AND METHOD FOR THE MANUFACTURE THEREOF", comprising: an active matrix 1 including a substrate 2, an array of transistors (not shown) and an array 3 of M.times.N connecting terminals, e.g., 4,4',4"; an array 5 of M.times.N piezoelectric actuators, e.g., 6,6',6", wherein each of the M.times.N piezoelectric actuators, e.g., 6, includes a piezoelectric member 7 having a top and a bottom surfaces, 8, 9, the top surface 8 being evenly separated by a trench 11 of a fixed depth and a centerline along a vertical direction, formed on the piezoelectric member 7, thereby generating a pair of actuating members 21,21', a signal electrode 12 located on the bottom surface 9 whose centerline along the vertical direction coincides with the centerline of the trench 11, and a pair of common reference electrodes, 13, 13', located on the separated top surface; an array 14 of M.times.N hinges, e.g., 15,15',15", each of the M.times.N hinges, e.g., 15, being provided with a top surface 16 and a bottom surface 17 having a protrusion 18 fitted to the trench 11 in each of the M.times.N piezoelectric actuators 6; and an array 19 of M.times.N mirrors, e.g., 20,20',20", wherein each of the M.times.N mirrors, e.g., 20, is mounted on the top surface 16 of each of the M.times.N hinges 15. The polarization directions of the piezoelectric material in the pair of actuating members 21,21' in each piezoelectric member 7, are opposite from each other.
In the above mentioned, copending, commonly owned application, there is also disclosed a method for manufacturing such an array of M.times.N piezoelectric actuated mirrors, the method comprising the steps of:
(1) obtaining a piezoelectric ceramic wafer having a top and a bottom surfaces; (2) forming an array of M.times.N signal electrodes on the bottom surface of the ceramic wafer and M+1 common reference electrodes on the top surface thereof; (3) mounting the ceramic wafer treated in accordance with above described step on an active matrix; (4) covering the M+1 common reference electrodes with M+1 photoresistive necked segments; (5) forming M trenches by using an etching method, wherein each of the M trenches, having a width of 50-70 .mu.m and a depth of 50-100 .mu.m, respectively, is located between two common reference electrodes and on the centerline of the signal electrodes, runs parallel to the common reference electrodes, is provided with a set of N-1 identically sized grooves, running perpendicular thereto; (6) forming a platform provided with a top surface by covering with an epoxy the entirety of the top surface of the ceramic wafer treated in accordance with above described steps, including the M trenches; (7) providing a light reflecting layer on the top surface of the platform, thereby forming a mirror layer, including the platform and the light reflecting layer; (8) patterning the mirror layer into an array of M.times.N mirrors; (9) removing the M+1 photoresistive necked segments; and (10) making electrical connections to thereby form the array of M.times.N piezoelectric actuated mirrors.
There is a number of problems associated with the above-described method for manufacturing an array of M.times.N electrodisplacive actuated mirrors, however. First of all, if the actuators are made of a piezoelectric material, in order for the array to function properly, the polarization directions thereof in the horizontally nearest neighboring actuators must be opposite from each other and those of the vertically nearest neighboring actuators must be the same. This is usually achieved by poling the piezoelectric material in two stages, which is an extremely difficult and also very cumbersome process.
Further, it is rather difficult and time consuming to form the M trenches, each trench having, as stated above, a width of 50-70 .mu.m and a depth of 50-100 .mu.m, precisely on the electrodisplacive material.
In addition, it is difficult to obtain a platform provided with a top surface which is trnely flat using the above described step (6), which in turn leads to an uneven light reflecting layer in the mirror layer.